What's the tranny gear for 3.73's on the Cobra?

[t_towner]

I know this has probably been asked a zillion times....

What spedo gear do I need purchase for the Cobra w/ 3.73's? Still have the 245/45ZR17's (25.7 in) but I'm not sure if the Cobra T5 has the same internal gear as the regular T5?

Surely there is a big thread about this? I've tried to search the forum but the search results keep crashing! :shrug:

Just need to know what part number to order?

Thanks!

 

[lone sailor]

21 tooth gear, red in color.

Part# C40Z-17271-A

 

[t_towner]

Great!! Thx :thumbsup:

Assume this is 100% correct gear and I don't have to change out the internal gear?

 

[BADBOYSPACK]

nope , just the speed sensor gear

 

[lone sailor]

Great!! Thx :thumbsup:

Assume this is 100% correct gear and I don't have to change out the internal gear?

As long as the internal tranny drive gear is the yellow E3ZZ-A then you're fine. If for some reason you have the green FOZZ-A then you won't be able to correct the speedo gear properly with a 3:73 gear/pinion set. You'll have to pull the tranny and swap the drive gear to the yellow gear.

 

[Orion1123]

The previous owner of my car put 3.55's in and didn't replace the speedo gear, so last week I replaced mine. I found them at www.50resto.com. If you download their catalog, on Pg. 102 they have a listing of different gears. It says that the red (21 tooth) is for 3.27 and the white (23tooth) is for the 3.55. For our stock transmssions there is not one listed for 3.73. They say that the trans drive gear will have to be changed for that gear set up. I have taken my car out on the expressway since the change and now my odometer is reading correctly, which leads me to believe that the new speedo gear is the corect one.

 

[lone sailor]

The previous owner of my car put 3.55's in and didn't replace the speedo gear, so last week I replaced mine. I found them at www.50resto.com. If you download their catalog, on Pg. 102 they have a listing of different gears. It says that the red (21 tooth) is for 3.27 and the white (23tooth) is for the 3.55. For our stock transmssions there is not one listed for 3.73. They say that the trans drive gear will have to be changed for that gear set up. I have taken my car out on the expressway since the change and now my odometer is reading correctly, which leads me to believe that the new speedo gear is the corect one.

Nothing against 50resto, but my information comes directly from Ford. It all depends on what tranny drive gear is installed. :bored:

 

[t_towner]

21 tooth gear, red in color.

Part# C40Z-17271-A

Just got the gear and will hopefully have it installed tonight. I have a cheap GPS system that can track MPH that i'll try to verify against.

 

[Orion1123]

Well, I installed the red one previously b/c that's what the ford dealer told me was the correct one, and that got me closer than the black one that was installed, but it still did not correct the problem. The white one worked for me though. t towner, let me know if the red works for you.

 

[lone sailor]

Well, I installed the red one previously b/c that's what the ford dealer told me was the correct one, and that got me closer than the black one that was installed, but it still did not correct the problem. The white one worked for me though. t towner, let me know if the red works for you.

That's cool man, I just wanted to let him know what Ford recommend and it's the internal tranny drive gear that will determine which speedo gear will properly correct it.

 

[montanagrog]

http://www.ddperformance.com/speedo_gear_chart.htm



Speedo Gear Chart



Axle Ratio 6T 7T 8T- Drive gears

Driven gears

2.73 - 16 18

3.08 - 18 20

3.27 16 19 21

3.55 17 20 -

3.73 18 21 -

4.10 20 - -

4.30 21 - -

4.56 - - -



Note: Calculated driven gears are based on normal mustang tires (815 revs/mile) and the formula listed below.



Driven Gear Teeth = Drive gear teeth x axle ratio x tire revs/mile
____________________________________
1000



Note: If the tire's are larger diameter than stock, go to the driven gear with (1) less tooth than calculated.



Type Trans 16T 17T 18T 19T 20T 21T

Manual wine white yellow pink black red

Automatic blue green gray tan orange purple



23T = White

23 T speedo gears are available, however they are not a ford gear. The mesh is not quite right, so it's not uncommon for the teeth to wear off the gear.

 

[BADBOYSPACK]

On my 92GT, when I dumped the OEM 3:27's out and went to 3:73 gears i had to put a ( C40Z-17271-A ) Ford part number in my AOD trans to make the speedo read correctly

I work at Ford and this gear was the correct one for the AOD and 3:73 gears

Montanagrog, great info on the gear choices !

 

[lone sailor]

I prefer Ford's chart better. It at least gives you the tranny drive gear combo information.......... http://www.fordracingparts.com/download/charts/129.pdf

 

[t_towner]

Just got the gear and will hopefully have it installed tonight. I have a cheap GPS system that can track MPH that i'll try to verify against.

Houston, we have a problem! :cryying:

Much better w/ the red 21 tooth but still not there?

I have this cheapie GPS system and the best I can figure...spedo is still showing approx 10mph faster then actual.

Here's the scooop. Interior tranny drive gear appears to be white (not yellow) but it was hard to tell b/c my light was crapping out. Tires are 245/45/17. I calc 785.35 revs per mile. White (er yellow) internal gear is a 7 tooth.

All this works out to a 20.5 tooth gear. Being a couple MPH off is fine, however 10?

What am I doing wrong here? :shrug:

BTW, pulled out a black gear.

 

[BADBOYSPACK]

you need to add a gear then drive with a new car then, because your not getting the gear thing

Its ok, just add the gear for what you are running, and go from there

 

[lone sailor]

Houston, we have a problem! :cryying:

Much better w/ the red 21 tooth but still not there?

I have this cheapie GPS system and the best I can figure...spedo is still showing approx 10mph faster then actual.

Here's the scooop. Interior tranny drive gear appears to be white (not yellow) but it was hard to tell b/c my light was crapping out. Tires are 245/45/17. I calc 785.35 revs per mile. White (er yellow) internal gear is a 7 tooth.

All this works out to a 20.5 tooth gear. Being a couple MPH off is fine, however 10?

What am I doing wrong here? :shrug:

BTW, pulled out a black gear.

Yes, the black gear you took out was for the stock gear ratio. The only way to properly correct the speedo is to change the tranny drive gear to the 7T drive gear.

 

[Lee]

The problem you're having is one of several reasons why I didn't go any higher than 3.55s in my 93, and if I remember correctly the "white" gear was correct for the 3.55s.

 

[Orion1123]

Since the white gear is not a Ford part are there problems with the teeath wearing down? If this is the case, will that mess up my transmission? Show I just go with the red gear and just know that the speedometer is off?

 

[montanagrog]

Dang chart didn't copy right!! I had a white 23 tooth driven gear in my 91, and it wore off. The teeth just started to slowly wrap over. Another friend had his teeth break off in pieces. There didn't seem to be any problems arise from the pieces, but then, he scattered the T5 after about 25,000 miles.

I had problems with the charts never showing the right gears and changing them 2-3 times to get close, and found the by counting the teeth on the drive gear, the color and teeth count didn't match to some charts. Then I accually measue circumfrence of the tires to enter in some of the formulas to get the rev/mile correct.

If you have a Stewart Warner speedometer dealer in town, they usaully have all the formulas to plug numbers in and gears. Mostly larger truck dealer have these.

 

[Lee]

I didn't have any trouble with my "white" gear wearing out, but then I didn't put very many miles on the car before selling it.